1. Field of Use
The present invention relates generally to a digital electronic controller for operating a power transmission which includes an engine-driven torque converter connected to a speed changing gear shift mechanism for transmitting power to, for example, the wheels of the vehicle, such as off-highway earth-moving machines in the 200 to 750 horsepower class.
2. Description of the Prior Art.
U.S. Pat. No. 3,805,640 issued Apr. 23, 1974, to Schneider et al for "Electronically Controlled Power Transmission" and assigned to the same assignee as the present application, discloses an engine-driven torque converter for driving a speed changing gear shift mechanism which transmits power to vehcile wheels. The torgue converter is provided with a lock-up clutch for connecting the torque converter into direct drive when engine speed is sufficiently high. Shifting in or out of clutch lock-up is controlled by a lock-up clutch valve which in turn is responsive to pressure conditions in a control valve on the gear shift mechanism. However, operation of the lock-up clutch valve can be inhibited by operation of a lock-up clutch solenoid valve. The gear shift mechanism is provided with sets of gears for different speed ranges and with clutches which are selectively operable to shift the mechanism into different speed ranges. These clutches are operated by solenoid controlled clutch valves. The torque converter is also provided with a solenoid operated retarder valve which automatically engages to effect retardation of the speed of the gear shift mechanism when the torque converter is direct drive and torque converter turbine speed exceeds engine high-idle speed. The retarder disengages after the lock-up clutch is signalled to disengage.
U.S. Pat. No. 3,805,640 discloses an analog type electronic controller which provides electrical output signals for actuation or non-actuation of the lock-up clutch solenoid valve, for actuation of the solenoids of the gear shift mechanism solenoid operated clutch valves and for actuation of the solenoid for the solenoid operated retarder valve. The prior art electronic controller receives electric input signals from a manually operable multiposition electric shift range selector switch; from an output speed sensor on the gear shift mechanism; from a turbine speed sensor on the torque converter (to effect retarder operation); and from an engine throttle position switch.
A transmission in accordance with U.S. Pat. No. 3,805,640 is capable of the following functions: automatic upshift or downshift to the selected speed range; automatic shifting to maintain appropriate speed in view of the speed range selected; automatic time delay in each speed range when upshifting or downshifting to speed ranges other than the next range to prevent hunting; downshifting or shift to neutral only when the correct speed range is reached; prevents any shifting to neutral unless that position is actually selected; prevents a shift reversal until a predetermined low speed is reached; inhibits lock-up in certain speed ranges; and performs other control functions.
The principle advantages of such a transmission are that it requires less skill on the part of the operator; it provides greater operating efficiency in that correct speed ranges are automatically selected and maintained; it reduces the possibility of damage to the transmission die to the use of incorrect operation procedures; and it increases the operating life of all transmission components due to the face that they operate within correct desired speed ranges and design limits.